After all of our testing and our results on the dynos from 1000hp capable stage 2's around 700hp to 500hp street 109 cars there are only 2 reasons I can conclude to go 3 bolt over 4 bolt. This is of coarse in applications over 500 rwhp. If you are not at minimum in the 10s or above that power level don't bother and stay 3 bolt style.
Only 2 reasons I can conclude:
1. Money (whether it be the small price difference and additional parts you need to switch up..or cause you already have most of the parts for 3 bolt style).
2. Racing in TSM to meet rule requirements.
I can't see any advantage to being 3 bolt other than the ability on here to buy and sell used parts and those main reasons listed above.
Sorry if any of this is repeated info but a few comparisons of a few 500-700hp tunes with 60/70 trim range billet turbos.
-Back pressure of the 3 bolt guys is around 2:1 or higher at around 24-30psi....where as 4 bolt guys are floating around a much nicer 1:1 / 1.3:1.
-Now this is not directly related to 3 bolt style cause you can still put a wastegate on the header with 3 bolt setup BUT then you must weld over the wastegate hole in the exhaust housing of the turbo etc etc....usually the 4 bolt setups and vbanded dp's put the wastegate where it should have been in the first place all along...on the headers. Controlling boost with these setups is impossible with an internally gated turbo....and pretty much impossible with even an external mounted in the buick fashion. My boost creep with a Tial 38mm and a Precision 6766 was really bad....and my buddy with a 44mm gate and a GTQ70 also had no chance of eliminating creep. This prevented me from using my standalones Dial a boost functions and we had to play around with the overboost shutoff since it was set to cut at +2psi.
-Also power increases are greater with the 4 bolt style as mentioned above depending on how far you are going with boost.
After dynoing my car with the 3 bolt setup I'm simply going to make the switch to 4 bolt at some point soon. Unless you are TSM or not making tons of power 3 bolt is simply a bottleneck. At what HP and boost levels is 3 bolt a true stop? Idk......that far we haven't gone yet. I'm sure the TSM guys have it written down somewhere in their secret recipe books